De-Gassing/ air removal

You can sparge it with an inert gas like helium. This is what is typically done with chromatographic solvents to remove more soluble gases. Something like this

is used to bring the gas into more intimate contact with the liquid.

What this process does is oust the dissolved air from the water; the helium has a low solubility, so it doesn't remain.

Thanks for that. Physically how is that achieved and are there units made that would dose the helium into tthe water? I am sorry but I dont quiet understand the concept.

I'm assuming you are using distilled or RO water. You will need some kind of reservoir to hold the water while it is being sparged - something like a 20-L plastic carboy, a cylinder of helium, a pressure regulator for the helium cylinder, some tubing - 1/2" polyethylene would probably be fine, and a metal frit (like the picture in my previous post).

• Fill the reservoir with the water you will be using
• Secure the regulator to the cylinder
• Attach a piece of tubing long enough to reach from the cylinder regulator to the bottom of the reservoir
• Attach the frit to the end of the tubing and lower it to the bottom of the reservoir
• Turn on the gas slowly and cautiously at first to find an acceptable flow rate
• Move the frit to different positions on the bottom of the carboy from time to time

You will have to test periodically for % dissolved gas (DG) to see how long it takes to sparge.

Once the DG levels are acceptable, turn off the Helium. The water is now ready to be fed to the autoclave.

Do not do this in an enclosed space as Helium can be an asphyxiant - use plenty of ventilation!

Mike

Ireland eng: do not add anything to the feedwater as suggested by a couple of the posts. If you do so then you will have to show that this does not have an effect of the sterilization process and that residues of this added substance does not have an impact either. The issue here is patient safety so I would suggest that you disregard these suggestions immediately.

Thank you for that but I am a validation test person and I know what is right and what is wrong but what I wanted to know was about degassing systems. Thanks anyway

Degassing in medical equipment (esp. dialysis) is usually done by pumping the water from a vessel under partial vacuum. I don't know if anyone makes this type of equipment for general use. Another method is to use ultrasound to induce cavitation in the liquid. The following company makes ultrasonic degassers: http://www.hielscher.com/ultrasonics/index.htm

also, this company that makes a degassing pump that should meet your flow requirements:

http://www.aquadevice.com/english/03pump_asp1.htm

Thank you . I will investigate further to see if we can apply to our situation.

My first instinct is this... Since you know heating it to 90C works for your situation (and other processes may or may not), go with that method. To address the feed pump cavitation, a small booster pump could be used to increase the suction pressure and provide the feed pump with adequate NPSH.

At what pressure are you operating your boiler? Pumping cold water into your boiler is not good for the boiler since you will be creating a thermal shock (expansion and contraction due to differing boiler water temperature). I suggest that you install a feed water deaeration system (where dissolved oxygen in the make-up water is removed and at the same time increase the feed water temperature to 100-103 deg. C.) Then change the feed water pump with a pump capable of pumping feed water up to 120 deg. C (i.e. Grundfos).

Ireland eng: I assume you are tying to meet the EN285 requirements for NCGs 3.5%(note that this is 35mL of gas per 1kg of steam, this equates to a NCG level of 0.0021% approximately). Since your water to the boiler is cold you will, as you have seen, have dissolved gasses. In this situation I would suggest that you try a membrane de-gasser visit www.liqui-cel.com for some details.

If the instruments being sterilised are wrapped then NCG's are of concern, however if they are unwrapped then the requirement for NCG's may not be that relevant. This is for you to decide. However if you are dealing with the IMB then perhaps it is better to fulfill the EN285 requirements for NCG's, Superheat and dryness as well.

Thank you I am a QTP and I know my criteria that I must operate to. My gasses are introduced by the water pump. I looked up liqui-cel and it fits the bill. Good answer , thank you.

I am not sure if this is practical for your application, but a method of deaerating water is to simply boil it and then allow it to cool down. When you boil water, as it heats up and not quite at the boiling point, you will notice a lot of air (oxygen and nitrogen gases) coming out of solution. If this water is cooled and then you reboil it, the bubbles will not be observed until you reach the degrees C boiling temperature. If you could prepare the autoclave water by first boiling and then storing this preboiled water in a sterile container ready for use, you will then have deaerated water on hand for the feed of the autoclave.

Thanks Kevinm but that is a little impractical but marks for offering a solution.

All my experience with autoclaves has been with industrial, lab or research applications. With the exception of the occasional ethylene Oxide unit. Those units either used the building steam supply or a self contained boiler. The one item that I wish to ask is: What is the reason for this specification? Sterilization is a function of time and temperature. Once you exceed 100 deg C, for a long enough time. Everything dies. My minimum is 120 deg C. the time is based upon what is to be autoclaved. Is this for the sterilization media, or is it to protect what is being autoclaved?

Icarus: You are correct in that sterilization is a function of time and temperature but only if the sterilization conditions are correct.

For dry heat sterilization the time is much longer and the and temperature is much higher (typically 170^oC for 2hours) than for Saturated Steam sterilization (the most common one probably being 121^oC for 15min's). The reason for the requirement for non-condensible gases (NCG's) is that the you do not wish to get dry heat conditions within the moist heat load - otherwise you will not get the appropriate conditions for sterilization. Its the difference between temperature and heat. In addition to the above the air can act as a barrier to heat transfer so yo may not even get the load item(s) up to temperature.

Now some steam sterilization cycles use an overpressure of air but this is not used for porous load applications where the NCGs are of concern.

Typically in the US and Canada the autoclave cycles are much longer and not as robust as the cycles developed in Europe (I suppose this is somewhat subjective)- the approach generally taken in the Canada and the US is to rely on the bio indicator kill, "bugs don't lie" approach. In Europe there is more emphasis on the cycle design, hence why air detectors, leak tests, air removal (sub and super atmospheric), steam penetration tests (BD tests) etc are much more common. I think this comes from the EN285 and the HTM2010 standards/ documents. The PDA TR1 document is some what of a watered down version of the previously two mentioned documents.

google air strippers , henry's law. but the systems i have delt with are not small

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